Projection lens system and projection image display apparatus using the same

ABSTRACT

When a projection lens system used for a rear projection type image display apparatus has a first lens group having an aspherical lens surface, a second lens group, a third lens group sharing almost all the positive refractive power of the overall system, a fourth lens group having an aspherical lens surface, a fifth lens group, and a sixth lens group including a lens having a profile of aspherical surface in which the concave surface thereof faces the screen side and the refractive power in the marginal area is weaker than the refractive power around the optical axis, a projection lens system having a large aperture ratio (low F-number), high focus, wide field angle, and sufficient marginal light amount ratio can be realized at a low cost. When a predetermined opening portion is formed in the projection lens and lens barrel, the lens elements are cooled by air suction and exhaust and the lowering of the lens performance due to temperature change can be prevented. When a flange is arranged in a suitable location of the opening portion, entry of a foreign material from the opening portion and light leakage from the inside are prevented and the contrast performance of the projection type image display apparatus can be prevented from lowering.

This application is a continuation of application Ser. No. 09/495,908,filed Feb. 2, 2000, now U.S. Pat. No. 6,243,211 which is a continuationof application Ser. No. 09/340,198, filed Jun. 28, 1999, now U.S. PatNo. 6,046,860 which is a continuation of application Ser. No.08/764,649, filed Dec. 11, 1996 now U.S. Pat. No. 5,946,142.

BACKGROUND OF THE INVENTION

The present invention relates to a projection lens system andparticularly to a projection lens system with a wide field angle whichprovides a bright image having an excellent focus performance even inthe marginal area, uses an inexpensive glass material, and has a shortprojection distance and a projection image display apparatus using thesystem which is excellent in cost performance.

Recently, a television set as an image display apparatus for home use isproceeding to a larger screen size as the wide aspect ratio increases.As an image display apparatus for home use, there are two typesavailable: a direct view type using a cathode ray tube and a so-calledprojection type for enlarging and projecting an image from a miniatureprojection tube, whose screen size is about 7 inches of (diagonal) via aprojection lens system. Due to restrictions concerning compactness andweight of a TV set, for a screen size of more than about 37 inch ofdiagonal, a projection image display apparatus is mainly used.

At first, this projection image display apparatus was inferior to thedirect view type in screen brightness and focus performance. However,recently, the performance of each of the components such as theprojection lens system, screen, and projection tube is improved, so thatboth the screen brightness and focus performance are approaching thoseof the direct view type. In the performance improvement process of theprojection image display apparatus, various arts have been developed inthe projection lens system which is a key device. First, to obtainscreen brightness equivalent to that of the direct view type or higher,as disclosed in U.S. Pat. No. 4,682,862, reduction of the F-number hasbeen tried by using many plastic aspherical lens elements.

Second a projection lens system has been developed for realizingimprovement of screen brightness and improvement of focus performance atthe same time . With respect to this projection lens system, asdisclosed in Japanese Patent Application Laid-Open No. 3-137610, thereis an example using a plastic aspherical lens and a doublet glass lens.As a result, in the current projection TV set, a projection lens systemhaving an F-number of about f/1.1 is used and both brightness and focusperformance are improved on the whole screen.

At the third step, a projection lens system with a wide field angle bywhich a compact set dimension can be realized on account of the shortprojection distance has been developed mainly. A reference describing anactual art for realizing a projection lens system with a wide fieldangle without reducing the brightness and focus performance in themarginal area and an actual projection lens system is disclosed inJapanese Patent Application Laid-Open No. 4- 5608. Hereinafter, the artdisclosed in this patent is referred to as a first prior art.

In this first prior art, by combining plastic aspherical lens elementsand glass lens elements effectively in a projection lens system of sixlens groups, the aforementioned problem is solved. Furthermore, theprojection lens system is structured so that almost all the positiverefractive power of the projection lens system is shared by the glasslenses and the plastic aspherical lens elements have little refractivepower, so that the peculiar drift of the focus performance due to atemperature change is reduced even if the plastic aspherical lenselements are used is reduced.

In this first prior art, the profile of the fluorescent face ofprojection tube has a curvature so that it is convex on the electron gunside. As a result, the projection lens system is structured so that thenormal of the fluorescent face in the marginal area is in the directionof the entrance pupil of the projection lens system and can fetch morelight fluxes in comparison with the case using a flat fluorescent face.Therefore, even if the field angle is widened, a relative illuminance ofa level which is almost no problem practically can be obtained in themarginal area.

The curvature of field is corrected by the lens element of the sixthlens group (hereinafter referred to as sixth lens). However, if thefluorescent face of projection tube has a curvature so that it is convexon the electron gun side, the generation amount of curvature of field isreduced and the focus performance in the marginal area is improved.

Furthermore, a projection lens system with a wide field angle whichrealizes a more excellent focus performance without reducing thebrightness in the marginal area and an actual art for realizing it aredisclosed in U.S. Pat. No. 5,272,540. Hereinafter, the art is referredto as a second prior art.

In the second prior art, a projection lens system having a constitutionof five groups by six elements is disclosed and the profile of thefluorescent face of projection tube which is an object is an asphericalprofile which is convex on the electron gun side. The curvature of theprofile in the marginal area is smaller than that in the neighborhood ofthe optical axis. By doing this, highly precise correction of thecurvature of field and astigmatism are compatible with each other andthe satisfactory focus performance and the light amount which issufficient practice are reserved in the marginal area of screen.

In this projection lens system, the lens element of the third lens group(hereinafter referred to as third lens) sharing almost all refractivepower of the overall lens system, has a concave lens of large dispersionglass and a convex lens of small dispersion glass stuck together; thechromatic aberration is corrected, and the large aperture (the F-numberis 0.96) and the high focus performance are compatible with each other.Furthermore, the combination of the lens element of the first lens group(hereinafter referred to as first lens) and the lens element of thesecond lens group (hereinafter referred to as second lens) offsets thelowering of the focus performance generated by deformation and expansionof each lens element due to temperature change and humidity change whichis an intrinsic problem when plastic lens elements are used.

On the other hand, in a conventional projection lens system, as a lensbarrel for assembling each lens element with high precision, a lensbarrel having the constitution disclosed in, for example, JapaneseUtility Model Application Laid- Open No. 2-51478 is often used. The lensbarrel of the prior art has an outer barrel and an inner barrel which isinstalled inside the outer barrel and can slide in the direction ofoptical axis of the lens without axial shift. The inner barrel isconstructed so that it can be divided into two parts longitudinally inthe direction of diameter of the lens along the optical axis of the lensand it has slits for holding a plurality of lens elements atpredetermined intervals with high precision on its inner surface.

In the aforementioned projection lens system having a constitution ofsix lens groups of the first prior art, there are several problems to besolved.

The first problem is caused by the lens constitution. In theaforementioned projection lens system, the third lens having negativerefractive power is arranged on the screen side of the lens element ofthe fourth lens group (hereinafter referred to as fourth lens) sharingalmost all the positive refractive power of the overall lens system. Thespherical aberration and coma aberration are corrected by the thirdlens.

Therefore, the location of the entrance pupil of the overall lens systemmoves to the screen side from the center of the fourth lens. As aresult, if an attempt is made to realize a wider field angle (reductionof the projection distance) in the aforementioned lens constitution,correction of the distortion and astigmatism becomes difficult.

Next, the second problem is a point that if an attempt is made to reducethe F-number or (increase the aperture ratio) of the projection lenssystem having this lens constitution and obtain a sufficient marginallight amount ratio, the apertures of the first, second, and third lensesbecome larger and the production cost increases.

The share of correction of each lens group in aberration correction ofthe aforementioned projection lens system is shown below.

The first lens is a spherical lens element of a meniscus profile havingpositive refractive power and corrects spherical aberration and comaaberration.

The second lens is a plastic aspherical lens element of a meniscusprofile having weak positive refractive power and corrects sphericalaberration and coma aberration.

The third lens is a spherical lens element having a weak divergentaction and corrects spherical aberration and coma aberration.

The fourth lens is a convex-convex glass spherical lens element having astrong convergent action.

Furthermore, the lens element of the fifth lens group (hereinafterreferred to as fifth lens) is a plastic aspherical lens element of ameniscus profile having weak positive refractive power and correctsastigmatism, distortion, and coma aberration.

The sixth lens has a constitution that it has a concave surface facingthe screen side, has negative refractive power accompanied by a liquidcoolant (A), and corrects curvature of field.

Among them, the second lens and fifth lens are a plastic aspherical lenselement and have a meniscus profile having weak positive refractivepower respectively. This projection lens system of prior art has aconstitution that each plastic lens element has little refractive powerand the peculiar shift of the focus performance due to a temperaturechange when the plastic aspherical lens element is used is reduced.

There is a third problem imposed that as mentioned above, in theprojection lens system using the first prior art, the applicable lensprofile of the plastic aspherical lens is limited to a specific profileand that the aberration correction cannot be attained sufficiently.

A fourth problem is also imposed that since four glass lens elements areincluded, the cost is increased.

Furthermore, the aspherical surface of the fifth lens is small, and thesixth lens is a glass lens element, whose screen side surface isspherical; so that correction of astigmatism and correction of curvatureof field are not compatible with each other.

Therefore, a fifth problem arises that correction of astigmatism in themarginal area is difficult.

In the first prior art, it is a subject (of the design) to solve theseproblems.

A problem of the projection lens system having a constitution of fivegroups by six elements to be solved in the second prior art is reductionin cost.

The two factors for an increase in the cost of the projection lenssystem are described below.

The first factor for an increase in cost is the profile of fluorescentface of the projection tube. The main profile of fluorescent face of theprojection tube is a spherical fluorescent face at present. When thisprojection lens system is applied, it is necessary to make the profileof fluorescent face aspherical and the projection tube is to be producedunder a special specification, so that it is a factor for an increase inthe cost of the set.

The second factor for an increase in cost is that it is essential to usea doublet lens comprising a large dispersion concave lens with a largediameter and a small dispersion convex lens with a large diameter whichare stuck together for the third lens so as to realize a large apertureratio (the F-number is 0.96) in this projection lens system and correctchromatic aberration satisfactorily.

Generally, the price of optical glass increases as the refractive indexincreases and as the dispersion decreases. In the second prior art, theoptical glass used as a third lens of the projection lens systemdescribed in Embodiment 1 includes large dispersion glass of SF11 andsmall dispersion glass of SK16. The prices of these optical glassmaterials are more than 2 times as expensive as the price of SK5 whichis typical of optical glass used in the projection lens system such thatthe price is 2.3 for SF11 and is 2.1 for SK16 (those glass names areabbreviations of Schott, Ltd. and often used in this field).

On the other hand, a problem when the aforementioned conventional lensbarrel is used in the projection lens system is that the air temperaturein the sealed space inside the lens barrel and the temperature of thelens elements rise, and the heated lens elements expands and deforms,and the focus performance of the projection lens system is loweredextremely.

As a result, it is a subject (of the design) to suppress rising of theair temperature in the sealed space inside the lens barrel and thetemperature of the lens elements and to prevent the lens elements fromexpansion and deformation even if the heat generated from an imagegenerating source is high.

SUMMARY OF THE INVENTION

An object of the present invention is to solve the problems of theprojection lens system of the prior art mentioned above and to provide aprojection lens system of a wide field angle which uses inexpensiveoptical glass, has an excellent focus performance even in the marginalarea even if the heat generated from an image generating source is high,obtains a bright image, and has a short projection distance and aprojection image display apparatus using the system which is excellentin cost performance.

To accomplish the above object, the projection lens system of thepresent invention uses technical means as described below.

Firstly, to solve the first and second problems of the first prior art,almost all the positive refractive power of the overall lens system isshared by the glass lens elements (hereinafter described as glass powerlens). In this case, a lens having negative refractive power is notarranged on the screen side of the lens group including the glass powerlens but a plastic aspherical lens element having weak positiverefractive power around the optical axis is arranged there. As a result,the entrance pupil does not move to the screen side from the glass powerlens, so that the first problem can be solved and a projection lenssystem with a wide field angle can be realized.

Furthermore, a light flux passing through the lens group including theglass power lens diverges and enters the lens groups positioned on thescreen side, so that the aperture of each of lens groups can be made assmall as possible and the second problem can be solved.

In the projection lens system of the present invention, to minimize thelowering of the focus performance due to temperature and humiditychanges, the refractive power of the plastic aspherical lens elementaround the optical axis is reduced to 30% of that of the glass powerlens or less.

The aberration depending on the aperture is corrected according to theprofile of lens surface including aspherical system in the area (themarginal area of the lens element) apart from the optical axis. Thesystem is structured so that the drift of the local refractive powerobtained according to the profile of lens surface including asphericalsystem in the marginal area of the lens due to temperature and humiditychanges is offset by combining a plurality of plastic aspherical lenselements. By doing this, the profile of lens element can be decidedwithout affecting aberration correction restrictively and the thirdproblem can be solved.

Many plastic aspherical lens elements having a lens surface includingstrong aspherical system can be used by the aforementioned technicalmeans, so that the number of glass lens elements can be reduced and thefourth problem can be solved.

To solve the fifth problem, a lens element having negative refractivepower with the concave surface facing the screen side is arranged in thelocation closest to the projection tube which is an image light source,and the lens surface of the lens element on the screen side is formed asan aspherical shape, and hence the astigmatism in the marginal area ofthe image is reduced. Furthermore, with respect to the lens elementarranged on the screen side of this lens element, the profile of lenssurface on the projection tube side is formed in a convex shape aroundthe optical axis and a concave shape on the projection tube side in themarginal area and hence the astigmatism in the marginal area of theimage can be reduced with higher precision.

To realize a reduction in cost which is a problem of the projection lenssystem having the constitution in the second prior art, the twofollowing means are used.

The first means is to form the fluorescent face of a projection tube tobe applied to the projection lens system as a spherical fluorescentface. When the fluorescent face of the projection lens system heaving aconstitution of five group by six elements described in the firstembodiment of the second prior art is changed to a spherical surface asit is, the length of optical path from an object point in the marginalarea on the fluorescent face to the exit surface of the fifth lens isdifferent between a beam of light passing through the saggital plane anda beam of light passing through the meridional plane, so that a greatdifference is generated in the focus performance between the saggitaldirection and the meridional direction because astigmatism conspicuouslyincreases in the marginal area. This trend is specially significant inthe marginal area between 90% of the distance (relative image heightfrom center to corner) from the center of the screen to each corner andeach corner.

Therefore, according to the present invention, the lens surface of thesixth lens having negative refractive power on the screen side is formedin a profile such that in the lens area traversed by the light flux froman object in the marginal area on the fluorescent face the lens action(divergent action) becomes weaker in comparison with that around theoptical axis of the therefore, the difference between the length ofoptical path on the saggital plane and that on the meridional plane isreduced. Furthermore, when in the lens element arranged on the screenside of the above-mentioned lens element having negative refractivepower, the profile of lens surface on the projection tube side is formedin a convex shape on the projection tube side around the optical axisand in a concave shape on the projection tube side in the marginal area,the difference of length of optical path can be made smaller and theastigmatism in the marginal area can be reduced remarkably.

The second means is to change the third lens to inexpensive opticalglass.

For that purpose, correction of chromatic aberration is realized by alarge dispersion plastic concave lens element and an inexpensive smalldispersion glass convex lens.

It is also effective to install a filter for cutting the spuriouscomponent other than the dominant wavelength component among the lightemission spectrum of a phosphorescent substance in at least one lenselement of the lenses constituting the projection lens system and reducethe generated chromatic aberration itself.

Furthermore, to realize a large aperture, the aforementioned largedispersion plastic concave lens element is formed in a profile of strongaspherical shape and the aberration is corrected with higher precision.Furthermore, the lens profile is formed in a concave meniscus profile inwhich the concave surface faces the screen side around the optical axisand particularly in a profile that with respect to the lens surface onthe projection tube side, the inclination of the lens surface in themarginal area of lens apart from the optical axis is increased. As aresult, the entrance height of light flux into the third lens (glass)can be decreased and the diameter of the third lens (glass) can be madesmaller when the same F-number is to be obtained, so that the cost canbe reduced.

On the other hand, the projection lens system of the present inventionis structured so that at least one communicating opening orcommunicating window extending outside of the projection lens systemfrom the spaces between the lens elements is installed.

Furthermore, at least one space among the spaces between the lenselements is structured so that the communicating opening orcommunicating window is arranged individually in each of at least twoleveling locations practically on the basis of the horizontal plane inthe operation status of the projection lens system or continuously overthose locations. In this case, the communicating opening orcommunicating window in the low location functions as an inlet of airand the communicating opening or communicating window in the highlocation functions as an outlet of air.

To install the communicating opening or communicating window, one of themethods (1) to (4) shown below is used or these methods are usedtogether.

(1) Around the connection point of a lens element holding member forholding at least one lens element and covering the spaces among the lenselements and a connection member for connecting the lens element holdingmember to the image generating source, a communicating opening orcommunicating window is arranged as a space surrounded by at least thelens element holding member and the connection member. In this case, itis possible that the volume of this space is restricted by the size ofprotrusion provided in the lens element holding member or the size ofprotrusion provided in the connection member.

(2) A communicating opening or communicating window is arranged in thelens element holding member itself.

(3) A lens element holding member comprising a first holding member forholding at least one lens element and a second holding member forfitting and holding the first holding member is structured and acommunicating opening or communicating window is arranged between thefirst holding member and the second holding member. In this case, atlease one groove provided in a concave shape on the inner side of thesecond holding member may be functioned as a communicating opening orcommunicating window.

(4) A communicating opening or communicating window is arranged aroundthe periphery of the lens element.

When a communicating opening or communicating window is arranged by oneof the aforementioned methods, it is desirable to set the space betweenthe lens element arranged closest to the image generating source among aplurality of lens elements and the lens element second closest to theimage generating source as a corresponding space.

The aforementioned communicating opening or communicating window isarranged so as to replace heated air in the spaces among the lenselements with air outside the projection lens system. In this case, newproblems may arise that a foreign material such as dust enters from thecommunicating opening or communicating window and adheres to the lenselements, or an external light enters the projection lens system and theimage contrast performance of the projection lens system is lowered, orwhen the projection lens system is used in a projection type imagedisplay apparatus, the image contrast performance of the projection typeimage display apparatus is remarkably lowered due to light leakage fromthe inside of the projection lens system.

To eliminate the problems, in the aforementioned projection lens system,in the opening portion of the communicating opening or communicatingwindow toward the outside of the projection lens system, a dust-proofmember, for example, a flange-shaped member is arranged in the way toprotect the air permeability. Or, the communicating opening orcommunicating window itself is formed in a bent, or curved, or twistedshape.

In the projection lens system of the present invention, theaforementioned communicating opening or communicating window functionsas an air inlet through which air at a low temperature (open air) isintroduced and an air outlet through which heated air is ejected in thespace among the lens elements in which the communicating opening orcommunicating window is provided. By doing this, the efficiency of heatradiation from the lens elements is increased by convection of air andthe lens elements are suppressed in rising of temperature and hence theexpansion and deformation due to rising of temperature are suppressedand as a result, the lens performance, particularly the focusperformance are prevented from lowering.

When a projection type cathode ray tube is used as an image generatingsource, the projection type cathode ray tube becomes a heat generatingsource. Therefore, when the aforementioned communicating opening orcommunicating window is provided in the space between the lens elementclosest to the projection type cathode ray tube and the lens elementsecond closest to it, the effect of the aforementioned action isremarkable. Air has a property that when it is heated, the specificgravity thereof decreases and it flows upward. Therefore, when theheight of location of the communicating opening or communicating windowwhich is used as an air outlet is set higher than the height of locationof the communicating opening or communicating window which is used as anair inlet on the basis of a certain horizontal plane, a practicallysufficient effect can be obtained in the aforementioned action.

On the other hand, when a dust-proof member is arranged in the openingportion of the communicating opening or communicating window toward theoutside of the projection lens system when the communicating opening orcommunicating window itself is formed in a bent, or curved, or twistedshape, entry of a foreign material or light into the projection lenssystem and light leakage from the inside of the projection lens systemcan be prevented. As a result, the contrast performance of theprojection lens system itself will not be lowered and neither will bereaduced the image contrast of the projection type image displayapparatus using the projection lens system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view showing the essential section of anembodiment of the projection lens system of the present invention;

FIG. 2 is a cross sectional view showing the arrangement of lenselements and outline of the ray tracing result in Embodiment 1 of theprojection lens system of the present invention;

FIG. 3 is a cross sectional view showing the arrangement of lenselements and outline of the ray tracing result in Embodiment 7 of theprojection lens system of the present invention;

FIG. 4 is a cross sectional view showing the arrangement of lenselements and outline of the ray tracing result in Embodiment 10 of theprojection lens system of the present invention;

FIG. 5 is a drawing showing the definition of the axes of coordinates inthe equation of the profile of lens surface;

FIG. 6 is an illustration for explaining differences between theaspherical surface and the spherical surface;

FIG. 7 is a characteristic diagram showing second derivative values ofthe function indicating the aspherical surface profile of the lenssurface of the sixth lens 6 on the screen side;

FIG. 8 is a characteristic diagram showing a deviation of the asphericalsurface profile of the lens surface of the sixth lens 6 on the screenside from the spherical surface profile;

FIG. 9 is an MTF characteristic diagram showing the focus performance ofEmbodiment 1 of the projection lens system of the present invention;

FIG. 10 is an MTF characteristic diagram showing the focus performanceof Embodiment 2 of the projection lens system of the present invention;

FIG. 11 is an MTF characteristic diagram showing the focus performanceof Embodiment 3 of the projection lens system of the present invention;

FIG. 12 is an MTF characteristic diagram showing the focus performanceof Embodiment 4 of the projection lens system of the present invention;

FIG. 13 is an MTF characteristic diagram showing the focus performanceof Embodiment 5 of the projection lens system of the present invention;

FIG. 14 is an MTF characteristic diagram showing the focus performanceof Embodiment 6 of the projection lens system of the present invention;

FIG. 15 is an MTF characteristic diagram showing the focus performanceof Embodiment 7 of the projection lens system of the present invention;

FIG. 16 is an MTF characteristic diagram showing the focus performanceof Embodiment 8 of the projection lens system of the present invention;

FIG. 17 is an MTF characteristic diagram showing the focus performanceof Embodiment 9 of the projection lens system of the present invention;

FIG. 18 is an MTF characteristic diagram showing the focus performanceof Embodiment 10 of the projection lens system of the present invention;

FIG. 19 is a characteristic diagram showing an example of general lightemission spectrum characteristics of green phosphorescent substance;

FIG. 20 is a cross sectional view showing the essential section of anexample of a projection lens system of the prior art;

FIG. 21 is a cross sectional view showing the essential section of the11th embodiment of the projection lens system of the present invention;

FIG. 22 is a cross sectional view showing the essential section when thecross section of the lens barrel 9 of the projection lens system shownin FIG. 21 is seen in the direction of the arrow A;

FIG. 23 is a cross sectional view showing the essential section of the12th embodiment of the projection lens system of the present invention;

FIG. 24 is a perspective view of the essential section showing theactual constitution of the first communicating opening 27 shown in FIG.23;

FIG. 25 is a cross sectional view showing the essential section of the13th embodiment of the projection lens system of the present invention;

FIG. 26 is a cross sectional view showing the essential section of the14th embodiment of the projection lens system of the present invention;

FIG. 27 is a cross sectional view showing the essential section of the15th embodiment of the projection lens system of the present invention;

FIG. 28 is a cross sectional view showing the essential section of thelongitudinal cross section of a rear projection type image displayapparatus using the projection lens system of the present invention;

FIG. 29 is a cross sectional view showing the essential section of thelongitudinal cross section of another embodiment of a rear projectiontype image display apparatus using the projection lens system of thepresent invention;

FIG. 30 is a cross sectional view showing the projection lens system ofthe rear projection type image display apparatus shown in FIG. 28 indetail; and

FIG. 31 is a cross sectional view showing the projection lens system ofthe rear projection type image display apparatus shown in FIG. 29 indetail.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The embodiments of the present invention will be explained hereunderwith reference to the accompanying drawings.

FIG. 1 is a cross sectional view showing the essential section of anembodiment of the projection lens system of the present invention.

In FIG. 1, numeral 1 indicates a first lens, 2 a second lens, 3 a thirdlens, 4 a fourth lens, 5 a 5 fifth lens, 6 a sixth lens, 7 a liquidcoolant, 8 a projection type cathode ray tube (hereinafter abbreviatedto projection tube) which is an image generating source, 8 a a facepanel of the projection tube, P1 a fluorescent face of the projectiontube, and 9 a lens barrel. The lens barrel 9 is separated into an innerbarrel 9 a and an outer barrel 9 b and the inner barrel 9 a includes thefirst lens to the fifth lens which are incorporated and is fixed to theouter barrel 9 b with a set screws 12. Furthermore, the outer barrel 9 bis fixed to a coupling bracket 11 via a holding plate 13 with screws(not shown in the drawing). The system is structured so as to enlargeand project an image on the fluorescent face of the projection tube P1which is an object surface on a screen 14.

Tables 1 to 10 (Embodiments 1, 2, 3 , . . . , and 10 are usedrespectively) show actual lens data which can be fetched by theprojection lens system of the present invention.

TABLE 1 f = 90.49 mm, F_(NO) = 0.96 Axial distance Abbe's number Radiusof between νd/refractive curvature RD surfaces index Screen Lens surface∞ 1042.6 1.0 1st lens S₁ 91.403 8.874 57.9/1.49334 S₂ 280.37 2nd lens S₃−596.50 15.473 1.0 S₄ −590.00 9.200 57.9/1.49334 3rd lens S₅ 81.0668.7068 1.0 S₆ −235.00 25.000 61.25/1.59137 4th lens S₇ −270.00 1.008 1.0S₈ −450.00 4.000 30.30/1.58890 5th lens S₉ 18535.00 10.80 1.0  S₁₀−225.00 8.400 57.9/1.49334 6th lens  S₁₁ −56.000 30.000 1.0  S₁₂ −58.0003.405 57.9/1.49334 Transparent ∞ 11.49 1.44704 medium Cathode-ray Face−350.00 14.10 1.56232 tube panel Fluorescent face P₁ Lens Surface CC AEAF AG AH 1st lens S₁ −14.205306 l.27801 × E-6 −1.35740 × E-9 3.77495 ×E-13 −3.40452 × E-17 S₂ 1.5000000 −9.32634 × E-8 1.54377 × E-10 −7.28237× E-14 2.08978 × E-17 2nd lens S₃ 8.0000000 2.38533 × E-6 1.25739 × E-10−1.02973 × E-13 2.20148 × E-17 S₄ 8.3999996 1.91166 × E-6 −5.03454 ×E-10 1.55701 × E-13 −1.27999 × E-l7 4th lens S₇ 0.0000 0.0000 0.00000.0000 0.0000 S₈ 0.0000 −l.74446 × E-7 l.55853 × E-10 −l.07123 × E-132.70771 × E-17 5th lens S₉ −15.300000 −2.64597 × E-7 l.96982 × E-9−1.17973 × E-12 l.13858 × E-16  S₁₀ 0.000 9.74735 × E-7 1.85426 × E-9−7.84582 × E-13 4.27076 × E-17 6th lens  S₁₁ 0.000 −1.34293 × E-67.37058 × E-l0 1.53851 × E-13 2.42038 × E-17$Z = {\frac{r^{2}/{RD}}{1 + \sqrt{1 - {\left( {1 + {CC}} \right){r^{2}/{RD}^{2}}}}} + {{AE} \cdot r^{4}} + {{AF} \cdot r^{6}} + {{AG} \cdot r^{8}} + {{AH} \cdot r^{10}}}$

TABLE 2 f = 90.31 mm, F_(NO) = 1.02 Axial distance Abbe's number Radiusof between νd/refractive curvature RD surfaces index Screen Lens surface∞ 1042.6 1.0 1st lens S₁ 85.301 8.874 57.9/1.49334 S₂ 248.10 2nd lens S₃−596.50 20.146 1.0 S₄ −590.00 9.200 57.9/1.49334 3rd lens S₅ 81.0664.933 1.0 S₆ −235.00 22.700 61.25/1.59137 4th lens S₇ −270.00 1.080 1.0S₈ −450.00 4.000 30.30/1.58890 5th lens S₉ 18535.00 10.80 1.0  S₁₀−241.19 8.400 57.9/1.49334 6th lens  S₁₁ −56.000 30.000 1.0  S₁₂ −58.0003.405 57.9/1.49334 Transparent ∞ 11.49 1.44704 medium Cathode-ray Face−350.00 14.10 1.56232 tube panel Fluorescent face P₁ Lens Surface CC AEAF AG AH 1st lens S₁ −14.205306 1.92669 × E-6 −1.85054 × E-9 5.75077 ×E-13 −6.05405 × E-17 S₂ 1.5000000 7.18758 × E-8 −4.05008 × E-10 2.13l88× E-13 l.61270 × E-17 2nd lens S₃ 8.0000000 2.07465 × E-6 4.74347 × E-116.19323 × E-14 −1.8l834 × E-17 S₄ 8.3999996 l.76511 × E-6 −2.71126 ×E-10 1.43099 × E-13 −2.74519 × E-17 4th lens 5₇ 0.0000 0.0000 0.00000.0000 0.0000 S₈ 0.0000 −3.76560 × E-7 1.20340 × E-10 −3.00848x5-146.05881x5-18 5th lens S₉ −15.300000 −2.64597 × E-7 1.96982 × E-9−l.l7973 × E-12 l.13858 × E-16  S₁₀ 0.000 l.16291 × E-6 l.80247xE-97.02182 × E-13 1.93070 × E-17 6th lens  S₁₁ 0.000 −1.59847 × E-61.35363xE-9 −6.40009 × E-13 1.66139 × E-16$Z = {\frac{r^{2}/{RD}}{1 + \sqrt{1 - {\left( {1 + {CC}} \right){r^{2}/{RD}^{2}}}}} + {{AE} \cdot r^{4}} + {{AF} \cdot r^{6}} + {{AG} \cdot r^{8}} + {{AH} \cdot r^{10}}}$

TABLE 3 f = 90.77 mm, F_(NO) = 1.01 Axial distance Abbe's number Radiusof between νd/refractive curvature RD surfaces index Screen Lend surface∞ 1042.6 1.0   1st lens S₁ 106.180 8.874  57.9/1.49334 S₂ 267.06 18.0751.0   2nd lens S₃ −1483.80 9.200  57.9/1.49334 S₄ −339.15 9.1674 1.0  3rd lens S₅ 76.594 22.700 61.25/1.59137 S₆ −235.00 1.080 1.0   4th lensS₇ −270.00 4.000 30.30/1.58890 S₈ −450.00 10.80 1.0   5th lens S₉18535.00 8.400  57.9/1.49334 S₁₀ −577.72 30.000 1.0   6th lens S₁₁−55.500 3.405  57.9/1.49334 S₁₂ −58.000 11.49 1.44704 Transparent ∞medium Cathode-ray Face 14.10 1.56232 tube panel Fluorescent face P₁−350.00 Lens Surface CC AE AF AG AH 1st lens S₁ −14.205306 −4.17615 ×E-7 −7.58755 × E-10 3.11083 × E-13 −3.26331 × E-17 S₂ 1.5000000 −1.25741× E-6 5.87530 × E-10 −1.83314 × E-13 3.84552 × E-17 2nd lens S₃8.0000000 2.05903 × E-6 7.77375 × E-10 −3.99801 × E-13 7.17568 × E-17 S₄8.3999996 1.58107 × E-6 3.39912 × E-10 −1.74104 × E-13 3.07068 × E-174th lens S₇ 0.0000 0.0000 0.0000 0.0000 0.0000 S₈ 0.0000 −5.47788 × E-73.08341 × E-10 −6.34311 × E-14 9.31559 × E-18 5th lens S₉ −15.300000−3.22064 × E-7 2.42981 × E-9 −1.69278 × E-12 2.46305 × E-16 S₁₀ 0.0001.58758 × E-6 2.05251 × E-9 −9.15005 × E-13 5.00000 × E-17 6th lens S₁₁0.000 −1.62384 × E-6 1.46180 × E-9 −6.25537 × E-13 1.79061 × E-16$Z = {\frac{r^{2}/{RD}}{1 + \sqrt{1 - {\left( {1 + {CC}} \right){r^{2}/{RD}^{2}}}}} + {{AE} \cdot r^{4}} + {{AF} \cdot r^{6}} + {{AG} \cdot r^{8}} + {{AH} \cdot r^{10}}}$

TABLE 4 f = 89.47 mm, F_(NO) = 1.00 Axial distance Abbe's number Radiusof between νd/refractive curvature RD surfaces index Screen Lens surface∞ 1042.6 1.0   1st lens S₁ 87.060 8.874  57.9/1.49334 S₂ 166.59 13.9071.0   2nd lens S₃ −737.56 9.200  57.9/1.49334 S₄ −188.83 10.482 1.0  3rd lens S₅ 90.712 22.700 61.25/1.59137 S₆ −235.00 1.080 1.0   4th lensS₇ −270.00 4.000 30.30/1.58890 S₈ −450.00 10.80 1.0   5th lens S₉18535.00 8.400  57.9/1.49334 S₁₀ −241.19 30.000 1.0   6th lens S₁₁−52.268 3.405  57.9/1.49334 S₁₂ −58.000 11.49 1.44704 Transparent ∞medium Cathode-ray Face 14.10 1.56232 tube panel Fluorescent face P₁−350.00 Lens Surface CC AE AF AG AH 1st lens S₁ −14.205306 1.81161 × E-6−1.81880 × E-9 4.93904 × E-13 −4.44977 × E-17 S₂ 1.5000000 4.78526 × E-7−5.76838 × E-10 3.61505 × E-13 −5.85045 × E-17 2nd lens S₃ 8.00000001.05968 × E-6 2.18392 × E-10 3.29367 × E-15 −9.38718 × E-18 S₄ 8.39999966.04039 × E-7 −1.05414 × E-10 2.82509 × E-14 1.17689 × E-17 4th lens S₇0.0000 0.0000 0.0000 0.0000 0.0000 S₈ 0.0000 −5.23821 × E-7 3.86150 ×E-11 3.41462 × E-16 1.15405 × E-18 5th lens S₉ −15.300000 −2.81921 × E-71.77440 × E-9 −1.02161 × E-12 1.07908 × E-16 S₁₀ 0.000 1.16291 × E-61.80247 × E-9 −7.02182 × E-13 1.93070 × E-17 6th lens S₁₁ 0.000 −8.30584× E-7 −3.19962 × E-10 7.06789 × E-13 −2.63143 × E-16$Z = {\frac{r^{2}/{RD}}{1 + \sqrt{1 - {\left( {1 + {CC}} \right){r^{2}/{RD}^{2}}}}} + {{AE} \cdot r^{4}} + {{AF} \cdot r^{6}} + {{AG} \cdot r^{8}} + {{AH} \cdot r^{10}}}$

TABLE 5 f = 90.13 mm, F_(NO) = 1.00 Axial distance Abbe's number Radiusof between νd/refractive curvature RD surfaces index Screen Lens surface∞ 1042.6 1.0   1st lens S₁ 112.98 8.874  57.9/1.49334 S₂ 415.40 17.2861.0   2nd lens S₃ −562.36 9.200  57.9/1.49334 S₄ −339.15 8.1494 1.0  3rd lens S₅ 76.594 22.700 61.25/1.59137 S₆ −235.00 3.080 1.0   4th lensS₇ −270.00 4.000 30.30/1.58840 S₈ −450.00 9.300 1.0   5th lens S₉18535.00 8.400  57.9/1.49334 S₁₀ −400.00 29.500 1.0   6th lens S₁₁−55.499 3.405  57.9/1.49334 S₁₂ −58.000 11.49 1.44704 Transparent ∞medium Cathode-ray Face 14.1 1.56232 tube panel Fluorescent face P₁−350.00 Lens Surface CC AE AF AG AH 1st lens S₁ 14.205306 −4.99132 × E-7−7.52281 × E-10 3.04572 × E-13 −3.17985 × E-17 S₂ 1.500000 −9.63142 ×E-7 −4.48452 × E-10 −1.48606 × E-13 3.24547 × E-17 2nd lens S₃ 8.0000002.70666 × E-6 3.50490 × E-10 −2.62215 × E-13 4.22459 × E-17 S₄ 8.3400002.08869 × E-6 −1.90134 × E-10 2.77475 × E-14 −1.42593 × E-17 4th lens S₇0.000000 −7.29331 × E-7 −1.99626 × E-10 6.48129 × E-15 −1.12055 × E-18S₈ 0.000000 −1.29715 × E-6 1.84357 × E-10 −1.46193 × E-13 2.60704 × E-175th lens S₉ −15.300000 −1.70710 × E-7 2.13023 × E-9 −1.37605 × E-121.09708 × E-16 S₁₀ 0.00000 1.58758 × E-6 2.05252 × E-9 −9.15005 × E-135.00000 × E-17 6th lens S₁₁ 0.000000 −1.89756 × E-6 1.72825 × E-91.08034 × E-12 3.39635 × E-16$Z = {\frac{r^{2}/{RD}}{1 + \sqrt{1 - {\left( {1 + {CC}} \right){r^{2}/{RD}^{2}}}}} + {{AE} \cdot r^{4}} + {{AF} \cdot r^{6}} + {{AG} \cdot r^{8}} + {{AH} \cdot r^{10}}}$

TABLE 6 f = 90.28 mm, F_(NO) = 1.00 Axial distance Abbe's number Radiusof between νd/refractive curvature RD surfaces index Screen Lens surface∞ 1050.0 1.0   1st lens S₁ 115.670 8.874  57.9/1.49334 S₂ 335.03 17.1621.0   2nd lens S₃ −1054.40 9.200  57.9/1.49334 S₄ −261.89 5.8105 1.0  3rd lens S₅ 71.717 22.700 61.25/1.59137 S₄ −325.88 2.267 1.0   4th lensS₇ −290.07 4.000 30.30/1.58890 S₈ 5000.00 9.300 1.0   5th lens S₉ 928.708.400  57.9/1.49334 S₁₀ −336.67 30.189 1.0   6th lens S₁₁ −54.636 3.405 57.9/1.49334 S₁₂ −58.000 11.49 1.44704 Transparent ∞ medium Cathode-rayFace 14.10 1.56232 tube panel Fluorescent face P₁ −350.00 Lens SurfaceCC AE AF AG AH 1st lens S₁ −14.898250 −7.47696 × E-7 −7.73792 × E-103.44880 × E-13 −3.75545 × E-17 S₂ 5.5688664 −1.09894 × E-6 5.28791 ×E-10 −2.05281 × E-13 4.66837 × E-17 2nd lens S₃ −2316.3117 2.54450 × E-65.62992 × E-10 −3.61632 × E-13 5.44320 × E-17 S₄ 11.690594 1.79735 × E-64.46261 × E-11 −1.10792 × E-13 6.60349 × E-18 4th lens S₇ 22.120667−5.45630 × E-7 −1.25450 × E-10 1.70354 × E-14 −1.41437 × E-17 S₈−719.55890 −1.28076 × E-6 1.68255 × E-10 −1.91393 × E-13 3.00716 × E-175th lens S₉ −15.300000 −4.49218 × E-7 1.60071 × E-9 −1.19463 × E-12−5.83877 × E-17 S₁₀ 0.00000 1.58758 × E-6 2.05251 × E-9 −9.15005 × E-135.00000 × E-17 6th lens S₁₁ −0.5923559 −1.91950 × E-6 1.26443 × E-9−7.45525 × E-13 2.90386 × E-16$Z = {\frac{r^{2}/{RD}}{1 + \sqrt{1 - {\left( {1 + {CC}} \right){r^{2}/{RD}^{2}}}}} + {{AE} \cdot r^{4}} + {{AF} \cdot r^{6}} + {{AG} \cdot r^{8}} + {{AH} \cdot r^{10}}}$

TABLE 7 f = 90.34 mm, F_(NO) = 1.00 Axial distance Abbe's number Radiusof between νd/refractive curvature RD surfaces index Screen Lens surface∞ 1050.0 1.0   1st lens S₁ 114.560 8.874  57.9/1.49334 S₂ 299.87 17.1621.0   2nd lens S₃ −866.97 9.200  57.9/1.49334 S₄ −239.70 5.0793 1.0  3rd lens S₅ 71.114 22.700 61.25/1.59137 S₆ −378.83 2.737 1.0   4th lensS₇ −287.97 4.000 30.30/1.58890 S₈ 4000.00 9.300 1.0   5th lens S₉ 613.068.400  57.9/1.49334 S₁₀ −344.07 30.312 1.0   6th lens S₁₁ −54.393 3.405 57.9/1.49334 S₁₂ −58.000 11.490 1.44704 Transparent ∞ mediumCathode-ray Face 14.10 1.56232 tube panel Fluorescent face P₁ −350.00Lens Surface CC AE AF AG AH 1st lens S₁ 13.429961 −8.40169 × E-7−7.76450 × E-10 3.51328 × E-13 −3.82801 × E-17 S₂ −3.3351539 −1.11543 ×E-6 5.31625 × E-10 −2.10620 × E-13 4.81196 × E-17 2nd lens S₃ −959.826742.58831 × E-6 5.51215 × E-10 −3.56294 × E-13 5.36534 × E-17 S₄ 10.3547691.80263 × E-6 7.19625 × E-11 −1.18864 × E-13 7.75962 × E-18 4th lens S₇22.120667 −5.45630 × E-7 −1.25450 × E-10 1.70354 × E-14 −1.41437 × E-17S₈ −3630.1763 −1.25638 × E-6 1.51585 × E-10 −1.90122 × E-13 3.04799 ×E-17 5th lens S₉ −15.300000 −4.18973 × E-7 1.51153 × E-9 −1.11826 × E-121.08743 × E-16 S₁₀ 0.000 1.58758 × E-6 2.05251 × E-9 −9.15005 × E-134.99999 × E-17 6th lens S₁₁ −0.0354248 −1.33128 × E-6 1.27556 × E-9−6.55222 × E-13 3.04020 × E-16$Z = {\frac{r^{2}/{RD}}{1 + \sqrt{1 - {\left( {1 + {CC}} \right){r^{2}/{RD}^{2}}}}} + {{AE} \cdot r^{4}} + {{AF} \cdot r^{6}} + {{AG} \cdot r^{8}} + {{AH} \cdot r^{10}}}$

TABLE 8 f = 90.10 mm, F_(NO) = 1.00 Axial distance Abbe's number Radiusof between νd/refractive curvature RD surfaces index Screen Lens surface∞ 1042.6 1.0   1st lens S₁ 110.91 8.874  57.9/1.49334 S₂ 393.88 17.4311.0   2nd lens S₃ −562.36 9.200  57.9/1.49334 S₄ −339.15 7.8423 1.0  3rd lens S₅ 76.594 22.700 61.25/1.59137 S₆ −235.00 2.080 1.0   4th lensS₇ −270.00 4.000 30.30/1.58840 S₈ −450.00 10.300 1.0   5th lens S₉18535.00 8.400  57.9/1.49334 S₁₀ −400.00 29.500 1.0   6th lens S₁₁−55.499 3.405  57.9/1.49334 S₁₂ −58.000 11.49 1.44704 Transparent ∞medium Cathode-ray Face 14.1 1.56232 tube panel Fluorescent face P₁−350.00 Lens Surface CC AE AF AG AH 1st lens S₁ −14.205306 −3.49264 ×E-7 −7.51764 × E-10 2.98572 × E-13 −3.16781 × E-17 S₂ 1.500000 −8.62273× E-7 4.44555 × E-10 −1.36020 × E-13 2.95057 × E-17 2nd lens S₃ 8.0000002.63183 × E-6 3.36531 × E-10 −2.58187 × E-13 4.36505 × E-17 S₄ 8.3400002.02573 × E-6 −2.24606 × E-10 2.83556 × E-14 −1.05000 × E-17 4th lens S₇0.000000 −5.45630 × E-7 −1.25450 × E-10 1.70354 × E-14 −1.41437 × E-17S₈ 0.000000 −1.02404 × E-6 2.45508 × E-10 −1.44920 × E-13 1.38124 × E-175th lens S₉ −15.300000 −7.06392 × E-7 2.06151 × E-9 −1.30794 × E-127.28924 × E-17 S₁₀ 0.00000 1.58758 × E-6 2.05252 × E-9 −9.15005 × E-135.00000 × E-17 6th lens S₁₁ 0.000000 −1.82729 × E-6 1.68806 × E-9−1.07491 × E-12 3.50966 × E-16$Z = {\frac{r^{2}/{RD}}{1 + \sqrt{1 - {\left( {1 + {CC}} \right){r^{2}/{RD}^{2}}}}} + {{AE} \cdot r^{4}} + {{AF} \cdot r^{6}} + {{AG} \cdot r^{8}} + {{AH} \cdot r^{10}}}$

TABLE 9 f = 90.33 mm, F_(NO) = 1.00 Axial distance Abbe's number Radiusof between νd/refractive curvature RD surfaces index Screen Lens surface∞ 1050.0 1.0   1st lens S₁ 109.780 8.874  57.9/1.49334 2nd lens S₃−562.36 9.200  57.9/1.49334 S₄ −339.15 10.013 1.0   3rd lens S₅ 76.59422.300 61.25/1.59137 S₆ −235.00 2.080 1.0   4th lens S₇ −270.00 4.00030.30/1.58890 S₈ −450.00 10.300 1.0   5th lens S₉ 18535.00 8.400 57.9/1.49334 S₁₀ −400.00 29.500 1.0   6th lens S₁₁ −55.499 3.405 57.9/1.49334 S₁₂ −58.000 11.49 1.44704 Transparent ∞ medium Cathode-rayFace 14.10 1.56232 tube panel Fluorescent face P₁ −350.00 Lens SurfaceCC AE AF AG AH 1st lens S₁ −14.205306 −3.77711 × E-7 −6.80543 × E-102.76889 × E-13 −2.92638 × E-17 S₂ 1.5000000 −9.39630 × E-7 5.48052 ×E-10 −1.69877 × E-13 3.37537 × E-17 2nd lens S₃ 8.0000000 2.50070 × E-64.30750 × E-10 −2.98735 × E-13 5.40955 × E-17 S₄ 8.4000000 1.94248 × E-6−1.45666 × E-10 −7.76624 × E-15 3.96630 × E-18 4th lens S₇ 0.000000−1.11617 × E-7 −2.69651 × E-11 −1.97791 × E-15 −1.56427 × E-17 S₈0.000000 −5.02307 × E-7 3.06274 × E-10 −1.28546 × E-13 −1.80677 × E-195th lens S₉ −15.300000 2.76587 × E-8 2.13667 × E-9 −1.35824 × E-121.19636 × E-16 S₁₀ 0.00000 1.58758 × E-6 2.05251 × E-9 −9.15005 × E-135.00000 × E-17 6th lens S₁₁ 0.00000 −1.62935 × E-6 1.40012 × E-9−7.34993 × E-13 2.07431 × E-16$Z = {\frac{r^{2}/{RD}}{1 + \sqrt{1 - {\left( {1 + {CC}} \right){r^{2}/{RD}^{2}}}}} + {{AE} \cdot r^{4}} + {{AF} \cdot r^{6}} + {{AG} \cdot r^{8}} + {{AH} \cdot r^{10}}}$

TABLE 10 f = 90.28 mm, F_(NO) = 1.00 Axial distance Abbe's number Radiusof between νd/refractive curvature RD surfaces index Screen Lens surface∞ 1042.6 1.0   1st lens S₁ 110.220 8.874  57.9/1.49334 S₂ 376.07 16.4781.0   2nd lens S₃ −562.36 9.200  57.9/1.49334 S₄ −339.15 8.9875 1.0  3rd lens S₅ 76.594 22.700 61.25/1.59137 S₆ −235.00 3.080 1.0   4th lensS₇ −270.00 4.000 30.30/1.58890 S₈ −450.00 9.300 1.0   5th lens S₉18535.00 8.400  57.9/1.49334 S₁₀ −400.00 29.500 1.0   6th lens S₁₁−55.499 3.405  57.9/1.49334 S₁₂ −58.000 11.490 1.44704 Transparent ∞medium Cathode-ray Face 14.10 1.56232 tube panel Fluorescent face P₁−350.00 Lens Surface CC AE AF AG AH 1st lens S₁ −14.205306 −6.05201 ×E-7 −7.33372 × E-10 3.22224 × E-13 −3.52762 × E-17 S₂ 1.5000000 −1.21465× E-6 6.09643 × E-10 −1.89740 × E-13 3.97475 × E-17 2nd lens S₃8.0000000 2.38762 × E-6 6.05052 × E-10 −3.78418 × E-13 5.98085 × E-17 S₄8.4000000 1.78170 × E-6 6.59630 × E-11 −1.20208 × E-13 1.50850 × E-174th lens S₇ 0.000000 −5.45630 × E-7 −1.25450 × E-10 1.70354 × E-14−1.41437 × E-17 S₈ 0.000000 −1.10393 × E-6 3.73070 '3 E-10 −2.13647 ×E-13 2.70690 × E-17 5th lens S₉ −15.300000 −3.51269 × E-8 2.02646 × E-9−1.25938 × E-12 8.23050 × E-17 S₁₀ 0.00000 1.58758 × E-6 2.05251 × E-9−9.15005 × E-13 4.99999 × E-17 6th lens S₁₁ 0.00000 −1.90908 × E-61.65847 × E-9 −9.59000 × E-13 2.77588 × E-16$Z = {\frac{r^{2}/{RD}}{1 + \sqrt{1 - {\left( {1 + {CC}} \right){r^{2}/{RD}^{2}}}}} + {{AE} \cdot r^{4}} + {{AF} \cdot r^{6}} + {{AG} \cdot r^{8}} + {{AH} \cdot r^{10}}}$

According to the embodiments of the present invention, the focal lengthof the single sixth lens and the focal length of the overall projectionlens system synthesizing every lens are calculated including the facepanel 8 a of the projection tube, the liquid coolant 7, and thefluorescent face P1.

FIGS. 2, 3, and 4 are cross sectional views showing the arrangement oflens elements and outline of the ray tracing result in the projectionlens system shown in Embodiments 1, 7, and 10 and the lens barrel andother components are omitted from reason of explanation. The lensprofile and arrangement shown in FIG. 4 are the same as those shown inFIG. 1.

The projection lens system used in the embodiments of the presentinvention is structured so that when rasters with a diagonal of 5.33inch are displayed on the fluorescent face of the projection tube P1 andenlarged and projected as image with a diagonal of 60 inch onto thescreen, a best performance can be obtained. The semi-field angle of theprojection lens system is 360 and a wide field angle is realized.Therefore, as described later, in a rear projection type image displayapparatus such as a projection television set having a constitution ofone reflecting mirror for folding the light path, a sufficiently compactset can be realized.

Next, how to read the lens data will be explained on the basis ofTable 1. Table 1 divides and displays data into spherical surface datamainly handling the lens area in the neighborhood of the optical axisand aspherical surface data in the marginal area thereof.

The table shows that the radius of curvature of the screen is infinity(that is, a plane), and the distance (axial distance between surfaces)on the optical axis from the screen to the surface S1 of the first lensl is 1042.6 mm, and the refractive index of the medium between them is1.0. The table also shows that the radius of curvature of the lenssurface S1 is 91.403 mm (the center of curvature is on the imagegenerating source side), and the distance (axial distance betweensurfaces) on the optical axis between the lens surfaces S1 and S2 is8.874 mm, and the refractive index of the medium between them is1.49334. In the same way, the table shows lastly that the radius ofcurvature of the fluorescent face P1 of the face panel 8 a of theprojection tube is 350 mm, and the thickness of the face panel of theprojection tube on the optical axis is 14.10 mm, and the refractiveindex thereof is 1.56232. The transparent medium described in each tableindicates the aforementioned liquid coolant 7.

With respect to the surfaces S1 and S2 of the first lens 1, the surfacesS3 and S4 of the second lens 2, the surfaces S7 and S8 of the fourthlens 4, the surfaces S9 and S10 of the fifth lens 5, and the surface S11of the sixth lens 6, aspherical coefficients are shown.

The aspherical coefficients are constants when the profile of lenssurface is expressed by the following equation. The exponent expressionin each table uses a base of 10. $\begin{matrix}\begin{matrix}{{Z(r)} = \quad {\frac{r^{2}/{RD}}{1 + \sqrt{1 - {\left( {1 + {CC}} \right){r^{2}/{RD}^{2}}}}} + {{AE} \cdot r^{4}} + {{AF} \cdot}}} \\{\quad {r^{6} + {{AG} \cdot r^{8}} + {{AH} \cdot r^{10}} + \ldots \quad + {A \cdot r^{2n}}}}\end{matrix} & \text{(Equation 1)}\end{matrix}$

where RD, CC, AE, AF, AG, AH, . . . , and A indicate arbitrary constantsand n indicates an arbitrary natural number. S5 and S6 indicate surfacesof the third lens 3. S13 indicates a surface of the face panel of theprojection tube and S12 indicates another surface of the sixth lens 6.

FIG. 5 is a drawing showing the definition of the axes of coordinates inEquation 1 of the aforementioned profile of lens surface, and thedirection of optical axis from the screen toward the image generatingsource is set as a Z axis, and the radial direction of lens is set as anr axis. In this case, Z(r) indicates the height of lens surface (surfacesag). r indicates the distance from the optical axis of the system, andRD indicates the radius of curvature, and CC indicates a conic constant.Therefore, when each coefficient such as CC, AE, AF, AG, and AH isgiven, the height of lens surface (hereinafter referred to as thesurface sag), that is, the profile is decided according to theaforementioned equation.

FIG. 6 is an illustration for explaining differences between theaspherical surface and the spherical surface. In FIG. 6, As(r) indicatesa value which is obtained by substituting the values of respectivecoefficients in Equation 1 of the profile of lens surface Z(r) and Ss(r)indicates a value when only the radius of curvature RD is substituted inEquation 1 of the profile of lens surface Z(r) and the othercoefficients are set to 0. As the absolute value of the ratio((As(r)−Ss(r))/Ss(r)) of the difference of these values (As(r)−Ss(r)) toSs(r) increases, the degree of the aspherical surface increases instrength.

The above is how to read the data shown in Table 1. With respect toTables 2 to 10, how to read is the same.

Next, the action of each lens group of the projection lens system of thepresent invention will be explained hereunder.

The first lens 1 has a concave profile in the marginal area as shown inFIGS. 2, 3, and 4 and corrects the spherical aberration for the lightflux (upper ray RAY1, lower ray RAY2) from an object A on the axis andthe coma aberration for the light flux (upper ray RAY3, lower ray RAY4)from an object B in the marginal area. The location (the marginal areaof the lens apart from the optical axis of the lens surface on thescreen side) through which the light from the upper ray RAY3 to thelower ray RAY4 passes has a profile of aspherical surface which isconcave on the screen side.

The second lens 2 has a profile of aspherical surface so that themarginal area of the lens remote from the optical axis of the lenssurface on the screen side is convex on the screen side as shown inFIGS. 2, 3, and 4 so as to correct astigmatism and coma aberration. Whenthis lens is combined with the first lens 1, the system is structured sothat the negative refractive power on the basis of the lens profile(concave) in the marginal area of the first lens and the positiverefractive power on the basis of the lens profile (convex) in themarginal area of the second lens offset each other. Therefore, even ifboth lens are plastic products, the lowering of the focus performance ofthe projection lens system due to changes in temperature and absorptionof moisture can be suppressed as much as possible.

The third lens 3 is made of glass so as to reduce the drift of the focusperformance due to temperature changes and structured so as to increasethe positive refractive power as much as possible. According to thisembodiment, to reduce the production cost of the projection lens system,SK5 which is inexpensive optical glass is used.

The fourth lens 4 has a meniscus profile which is concave on the screenside as shown in FIGS. 2, 3, and 4 or a lens profile which is concave onboth sides (the embodiments shown in Tables 6 and 7) in the center areathereof and has an aspherical surface profile which is a meniscusprofile which is concave on the screen side in the marginal areathereof.

For the light flux (upper ray RAY1, lower ray RAY2) from the objectpoint A on the axis, the fourth lens 4 corrects the spherical aberrationby the concave profile in the marginal area of lens/and reduces thechromatic aberration in combination with the third lens 3 by using ahigh dispersion material having an Abbe's number of 45 or less.

On the other hand, the fourth lens 4 of the present invention is a lenselement with an almost uniform thickness as a whole due to theaforementioned aspherical surface profile and for example, even if aplastic material having poor fluidity for molding such as PC(polycarbonate) is used, a high profile accuracy can be obtained.Furthermore, the lens profile of the fourth lens 4 is a lens profilethat the neighborhood of the optical axis has a concave meniscus profilewhose concave surface faces the screen side and that particularly withrespect to the lens surface on the projection tube side, the inclinationof the lens surface in the marginal area of lens apart from the opticalaxis is large and the lens surface is almost parallel with the lenssurface on the screen side. As a result, as shown in FIGS. 2 to 4, theupper ray (RAY1, RAY2) of the light flux generated from the object pointA on the optical axis can be shifted toward the optical axis. Therefore,the light entry height into the third lens (glass) is lowered and thediameter of a glass lens can be smaller than that is when the sameF-number is obtained without the fourth lens. As a result, the cost of aglass lens can be reduced.

Furthermore, since the inclination of the lens surface in the marginalarea of the fourth lens 4 is large, the incident angle into the thirdlens 3 is increased and the refractive power of the third lens 3 isdecreased. Therefore, an inexpensive glass material with a refractiveindex nd of 1.6 or less can be used for the third lens and the cost canbe reduced.

The fifth lens 5 corrects coma aberration of higher order generated bythe light flux (upper ray RAY3, lower ray RAY4) from the object point Bin the marginal area as shown in FIGS. 2, 3, and 4, so that the profilein the neighborhood of the location (the marginal area of the lenssurface on the projection tube side which is an image generating source)through which the lower ray RAY4 passes is an aspherical surface profilewhich is concave on the projection tube side. The profile in theneighborhood of the location through which the upper ray RAY3 passes isalso an aspherical surface profile which is concave locally on thescreen side.

Therefore, the lens surface of this lens on the projection tube side hasan aspherical surface profile in which the neighborhood of the opticalaxis is convex on the projection tube side and the marginal area isconcave on the projection tube side as a whole. To suppress the loweringof the focus performance of the projection lens system due to changes intemperature and absorption of moisture as much as possible, therefractive power is made as small as possible.

The sixth lens 6 corrects the curvature of field accompanied by thefluorescent face P1. The fluorescent face P1 is a spherical fluorescentface unlike the prior art 2, so that as shown in FIGS. 2, 3, and 4, theaspherical surface profile of the lens surface of the sixth lens 6 onthe screen side is a profile that the refractive power in the areathrough which the light flux (upper ray RAY3, lower ray RAY4) from theobject point B in the marginal area passes is weaker than the refractivepower in the neighborhood of the optical axis and the sixth lens 6corrects the astigmatism at the same time.

FIG. 7 is a characteristic diagram in which values obtained bysubstituting a distance of r from the optical axis in a secondderivative obtained by differentiating the function indicating theprofile of aspherical surface of the lens surface of the sixth lens 6 onthe screen side quadratically are graphed. On the lens surfaces by thefirst prior art (prior art 1) and the second prior art (prior art 2)mentioned above, the absolute values of derivative values between theoptical axis and the marginal area of the lens increase monotonically.This shows that the refracting action of the lens increasesmonotonically from the optical axis toward the marginal area of thelens. On the other hand, in the embodiments of the present invention, avalue obtained in the same way has a point of inflection as shown inEmbodiment 8 or reduces in an area more than 70% of the effective radiusas shown in Embodiments 9 and 10. As a result, it is found that therefracting action of the lens increases once from the optical axistoward the marginal area and decreases thereafter.

FIG. 8 is a characteristic diagram in which the distance of theaspherical surface profile of the lens surface of the sixth lens 6 onthe screen side from the lens surface Ss(r) only of the sphericalsurface system is obtained by calculation. The horizontal axis shown inFIG. 8 indicates a relative value of the aforementioned distance r tothe effective lens radius and the vertical axis indicates a differencebetween As(r) and Ss(r). In comparison with the first prior art (priorart 1 shown in the drawing), in the embodiments of the presentinvention, the difference between As(r) and Ss(r) is small such as about½ of that in prior art 1 or less and the marginal area of the sixth lens6 is not thick but almost uniform in thickness, so that satisfactorymoldability can be obtained.

FIGS. 9 to 18 are characteristic diagrams showing evaluation results ofthe focus performance by the MTF (modulation transfer function) whenrasters with a diagonal of 5.33 inch are displayed on the fluorescentface of the projection tube using the aforementioned projection lenssystem of the present invention and enlarged and displayed on the screen(60 inch) and correspond to Embodiments 1, 2, 3, . . . , and 10sequentially. The horizontal axis in these drawings indicates a relativeimage height from center on the screen.

As a spatial frequency as an evaluation condition, a case that 300 TVlines are taken as a stripe signal of white and black on the screen,that is, 150 pair lines are taken for the longitudinal dimension of thescreen is shown. As shown in these drawings, by the projection lenssystem having this constitution, a satisfactory MTF characteristic canbe obtained.

On the other hand, when three primary-color projection tube of red,green, and blue are used as projection tubes which is image generatingsources, the spurious component other than the dominant wave lengthcomponent is generally included in the light emission spectrum of thephosphorescent substance of each projection tube.

FIG. 19 is a characteristic diagram showing an example of the lightemission spectrum of a general green phosphorescent substance. In thegreen light emission spectrum shown in FIG. 19, a spurious component ofseveral wave lengths can be seen in addition to a dominant wave lengthcomponent of 545 nm.

If a filter for cutting the aforementioned spurious component isinstalled in at least one of the lens elements constituting theprojection lens system so as to reduce the generated chromaticaberration itself, a more satisfactory focus performance can beobtained.

Next, power distribution to each lens group in the aforementionedembodiments of the projection lens system of the present invention willbe explained.

Table 11 is a table showing power distribution when the focal length ofthe overall projection lens system is assumed as f0 and the focallengths of the first lens 1, second lens 2, third lens 3, fourth lens 4,fifth lens 5, and sixth lens 6 are assumed as f1, f2, f3, f4, f5, and f6respectively in the embodiments of the present invention shown in Tables1 to 10.

The ranges of power distribution shown in Table 11 are shown below.

0.24<f0/f1<0.35

0.0<f0/f2<0.18

0.78<f0/f3<0.91

−0.20<f0/f4<0.0

0.0<f0/f5<0.21

−0.61<f0/f6<−0.55

According to this embodiment, by sharing the greater part of thepositive refractive power of the overall projection lens system by thethird lens which is a glass lens element, the drift of the focusperformance by temperature change is reduced.

TABLE 11 Focal length Lens Lens power distribution f₀ No. f₀/f₁ f₀/f₁f₀/f₃ f₀/f₄ f₀/f₅ f₀/f₆ (mm) 1 0.3343 0.00121 0.8617 −0.0783 0.2008−0.5550 90.486 2 0.3489 0.00121 0.8624 −0.0781 0.1871 −0.5544 90.310 30.2587 0.1021 0.9041 −0.0785 0.0799 −0.5640 90.775 4 0.2510 0.17490.7875 −0.0774 0.1854 −0.6037 89.473 5 0.2893 0.0527 0.8977 −0.07800.1135 −0.5602 90.130 6 0.2555 0.1283 0.8889 −0.1940 0.1798 −0.573490.276 7 0.2442 0.1352 0.8755 −0.1981 0.2016 −0.5773 90.339 8 0.29090.0527 0.8974 −0.0780 0.1135 −0.5600 90.098 9 0.2936 0.0529 0.9001−0.0782 0.1138 −0.5614 90.330 10  0.2888 0.0528 0.8992 −0.0781 0.1138−0.5611 90.277 f₀: Focal length of overall lens system (mm) f₁: Focallength of first lens (mm) f₂: Focal length of second lens (mm) f₃: Focallength of third lens (mm) f₄: Focal length of fourth lens (mm) f₅: Focallength of fifth lens (mm) f₆: Focal length of sixth lens (mm)

Next, characteristics of the profile of lens surface will be explained.

The profiles of aspherical surfaces of the lens surface S1 of the firstlens 1 on the screen side, the lens surface S8 of the fourth lens 4 onthe image generating source side, the lens surface S10 of the fifth lens5 on the image generating source side, and the lens surface S11 of thesixth lens 6 on the screen side have the following characteristics.

In FIG. 6, As(r) indicates a value which is obtained by substituting thevalues of respective coefficients in Equation 1 of the profile of lenssurface Z(r) and Ss(r) indicates a value when only the radius ofcurvature RD is substituted in Equation 1 of the profile of lens surfaceZ(r) and the other coefficients are set to 0. In this case, the value ofAs(r)/Ss(r) is assumed as an index indicating the degree of theaspherical surface. In this case, the aforementioned ratio of As and Ssof the lens surface S1 of the first lens 1 on the screen side is withinthe following range as shown in Table 12.

(As/Ss)>−0.1

The aforementioned ratio of As and Ss of the lens surface S8 of thefourth lens 4 on the image generating source side is within thefollowing range as shown in Table 13.

(As/Ss)>−21.2

Furthermore, the aforementioned ratio of As and Ss of the lens surfaceS10 of the fifth lens 5 on the image generating source side is withinthe following range as shown in Table 14.

(As/Ss)<−0.6

Furthermore, the aforementioned ratio of As and Ss of the lens surfaceS11 of the sixth lens 6 on the screen side is within the following rangeas shown in Table 15.

(As/Ss)<1.1

Next, the condition for making the light amount ratio of the middlefield of the screen satisfactory and some other conditions will bedescribed. Assuming the distance (axial distance between surfaces) onthe optical axis between the first lens 1 and the second lens 2 as L12,the ratio of it to the focal length f0 of the overall projection lenssystem relates to the light amount in the middle field of the screen andthe following relation is held as shown in Table 16.

(L 12/f0)<0.25

Beyond this range, the light amount ratio of the middle field of thescreen area is reduced.

The ratio of the distance (axial distance between surfaces) L 12 on theoptical axis between the first lens 1 and the second lens 2 to thedistance (axial distance between surfaces) L 23 on the optical axisbetween the second lens 2 and the third lens 3 is decided by the balanceof correction of aberration and the following relation is held as shownin Table 16.

(L12/L23)>1.3

Below this range, no satisfactory focus performance can be obtained.

Between the absolute value of radius of curvature Ra3 of the lenssurface S5 of the third lens 3 on the screen side and the absolute valueof radius of curvature Rb3 of the lens surface S6 of the third lens 3 onthe image generating source side, the following relation is held:

|Ra3|<|Rb3|

The reason is that the spherical aberration and coma aberration causedby the third lens 3 are reduced. Between the absolute value of radius ofcurvature Ra4 of the lens surface S7 of the fourth lens 4 on the screenside and the absolute value of radius of curvature Rb4 of the lenssurface S8 of the fourth lens 4 on the image generating source side, thefollowing relation is held:

|Ra4|<|Rb4|

The reason is that the reduction in the share of the positive refractivepower to the third lens 3 and the correction of chromatic aberration andspherical aberration are balanced. When a material of an Abbe's numberof 45 or less is used for the fourth lens 4, the chromatic aberrationcan be reduced.

The characteristics of the profile of lens surface are mentioned aboveon the basis of the lens data of the projection lens system in theembodiments of the present invention.

In this embodiment, the aspherical surfaces using up to the asphericalcoefficient of 10th order AH are described. Needless to say, aconstitution that a coefficient of 12th order or higher is included isalso included in the present invention.

TABLE 12 Effective radius of Lens Lens surface S₁ surface S₁ No. As (mm)Ss (mm) As/Ss (mm) 1 6.861 19.164 0.358 56.0 2 8.846 18.227 0.485 52.7 32.023 15.968 0.127 56.0 4 6.381 17.763 0.359 52.7 5 0.773 14.855 0.05256.0 6 −0.402 14.460 −0.028 56.0 7 −0.693 14.620 −0.047 56.0 8 1.80115.176 0.119 56.0 9 2.397 15.358 0.156 56.0 10  1.074 15.286 0.070 56.0As: Aspherical surface sag amount (mm) Ss: Spherical surface sag amount(mm)

TABLE 13 Effective radius of Lens Lens surface S₈ surface S₈ No. As (mm)Ss (mm) As/Ss (mm) 1 −2.759 −2.461 1.121 47.0 2 −2.386 −1.781 1.340 40.03 −2.239 −1.781 1.257 40.0 4 −2.950 −1.781 1.656 40.0 5 −5.032 −1.7812.825 40.0 6 −3.409 0.161 −21.18 40.1 7 −3.376 0.201 −16.80 40.1 8−4.202 −1.781 2.359 40.0 9 −2.657 −1.781 1.492 40.0 10  −4.196 −1.7812.356 40.0 As: Aspherical surface sag amount (mm) Ss: Spherical surfacesag amount (mm)

TABLE 14 Effective radius of Lens Lens surface S₁₀ surface S₁₀ No. As(mm) Ss (mm) As/Ss (mm) 1 2.389 −3.955 −0.604 42.0 2 2.621 −3.340 −0.78540.0 3 5.613 −1.386 −4.050 40.0 4 2.621 −3.340 −0.785 40.0 5 4.994−2.005 −2.491 40.0 6 3.675 −2.151 −1.709 38.0 7 3.721 −2.105 −1.767 38.08 4.994 −2.005 −2.491 40.0 9 4.994 −2.005 −2.491 40.0 10  4.994 − 2.005−2.491 40.0 As: Aspherical surface sag amount (mm) Ss: Spherical surfacesag amount (mm)

TABLE 15 Effective radius of Lens Lens surface S₁₁ surface S₁₁ No. As(mm) Ss (mm) As/Ss (mm) 1 −20.744 −19.534 1.062 42.5 2 −18.823 −17.8561.054 41.0 3 −18.330 −18.094 1.013 41.0 4 −21.605 −19.850 1.088 41.0 5−19.314 −18.094 1.067 41.0 6 −17.858 −18.524 0.964 41.0 7 −17.680−18.650 0.948 41.0 8 −19.111 −18.094 1.056 41.0 9 −19.132 −18.094 1.05741.0 10  −19.542 −18.094 1.080 41.0 As: Aspherical surface sag amount(mm) Ss: Spherical surface sag amount (mm)

TABLE 16 Axisal distance Lens Focal length between lenses No. f₀ (mm)L₁₂ (mm) L₂₃ (mm) L₁₂/L₂₃ L₁₂/f₀ 1 90.486 15.473 8.707 1.777 0.171 290.310 20.146 4.933 4.084 0.223 3 90.775 18.075 9.167 1.972 0.199 489.473 13.907 10.482 1.327 0.155 5 90.130 17.286 8.149 2.121 0.192 690.276 17.162 5.811 2.954 0.190 7 90.339 17.162 5.079 3.379 0.190 890.098 17.431 7.842 2.223 0.194 9 90.330 16.778 10.013 1.676 0.186 10 90.277 16.478 8.988 1.833 0.183 L₁₂: Axial distance between first lensgroup and second lens group L₂₃: Axial distance between second lensgroup and third lens group f₀: Focal length of overall projection lenssystem

Next, a method that in the projection lens system of the presentinvention, at least one communicating opening or communicating windowextending outside of the projection lens system from the spaces betweenthe lens elements is installed and that even if the heat quantitygenerated from the image generating source is large, the air temperaturein the sealed space inside the lens barrel and the temperature of thelens elements are prevented from rising will be explained.

FIG. 20 is a cross sectional view showing the essential section of anexample of a projection lens system of the prior art.

In FIG. 20, numeral 17 indicates a projection lens system, 8 aprojection type cathode ray tube as an image generating source, 7 aliquid coolant, 20 lens elements, 9 a lens barrel as a lens elementholding member, 11 a bracket as a connection member, and 10 elasticbodies. The lens barrel 9 has an inner barrel 9 a and an outer barrel 9b and the lens elements 20 except the lens element 20 a which is closestto the projection type cathode ray tube 8 are held in the inner barrel 9a with high precision. Both the lens element 20 a and the projectiontype cathode ray tube 8 are pressed and held by the bracket 11 by asuitable holding means via the elastic bodies 10 and the liquid coolant7 is sealed in the space surrounded by the lens element 20 a, theprojection type cathode ray tube 8, and the bracket 11. At this time,the inside of the lens barrel 9 is a sealed structure practically. As aresult, by the heat generated by the projection type cathode ray tube 8which is an image generating source, the lens element 20 a closest tothe projection type cathode ray tube 8 and the air in the space betweenthe lens element 20 a and the lens element 20 b second closest to theprojection type cathode ray tube 8 are heated sequentially andfurthermore, the temperature of the overall lens elements 20 and the airtemperature in the sealed spaces between the lens elements risegradually. This heat is radiated outside the projection lens system 17almost only by heat transfer from the outer surface of the bracket 11,the outer surface of the lens barrel 9, and the outer surface of thelens element farthest away from the projection type cathode ray tube 8among the lens elements 20. However, the material of lens elements isgenerally glass or plastics and when the lens barrel 9 is made ofplastics from the point of view of moldability, the heat transfercoefficient from these outer surfaces is smaller than the heat transfercoefficient from the metal surface, so that the heat radiation amount issmaller than the exothermic amount of the projection type cathode raytube 8 and others and the air temperature in the sealed spaces and thetemperature of the lens elements rise furthermore. As a result, aproblem arises that the heated lens elements are expanded or deformedand hence the focus performance of the projection lens system isextremely lowered. Therefore, it is a subject for design to suppressrising of the air temperature in the sealed space in the lens barrel andthe temperature of the lens elements and to prevent the lens elementsfrom expansion and deformation even if the heat quantity from the imagegenerating source is large.

FIG. 21 is a cross sectional view showing the essential section of the11th embodiment of the projection lens system 17 of the presentinvention and the same numeral is assigned to the part which isequivalent to a part shown in FIG. 20. The lens barrel 9 has an innerbarrel 9 a and an outer barrel 9 b holding the inner barrel 9 a in theslidable state and the lens elements 20 except the lens element 20 awhich is closest to the projection type cathode ray tube 8 are held inthe inner barrel 9 a with high precision.

In FIG. 21, in the outer barrel 9 b of the lens barrel 9, at least onecommunicating opening (a communicating window when the overall length Orthe opening is short) 27 for connecting the inside of the lens barrel 9and the outside of the projection lens system is installed.

FIG. 22 is a cross sectional view showing the essential section when thecross section of the lens barrel 9 of the projection lens system 17shown in FIG. 21 is seen in the direction of the arrow A. The innerbarrel 9 a is fitted and held by a plurality of fitting protrusions 25installed on the inner surface of the outer barrel 9 b and grooves 28 abetween the fitting protrusions 25 become a second communicating opening28. In FIG. 22, the fitting protrusions 25 on the inner surface side ofthe outer barrel 9 b are structured so that they are arranged at fourlocations on a cross section perpendicular to the optical axis. However,the present invention is not limited to this constitution. For example,the number of arrangement locations of the fitting protrusions 25 may be3 or any other number. These fitting protrusions 25 may be in a shapethat they are cut into pieces in the direction of the optical axis andany constitution that the inner barrel 9 a can slide inside the outerbarrel 9 b smoothly and that the grooves 28 a can fulfill the functionas a communicating opening fully is acceptable.

In this constitution, when the projection lens system is actually used,for example, when it is incorporated and used in a rear projection typeimage display apparatus, the right side (the projection type cathode raytube side) of FIG. 21 is generally located low and the left side (thelens element side) is generally located up, so that the location of thesecond communicating opening 28 is generally higher than the location ofthe first communicating opening 27. Therefore, low-temperature air C(open air) introduced from the first communicating opening 27 is heatedby the projection type cathode ray tube 8 in the space between the lenselement 20 a closest to the projection type cathode ray tube 8 and thelens element 20 b second closest to it, and the temperature thereofrises, and the air becomes light due to volume expansion. Air H which isheated and lightened flows out of the second communicating opening 28.The lens elements 20 radiate heat efficiently by repetition of thisseries of phenomena, so that the expansion and deformation thereof canbe suppressed and the focus performance of the projection lens systemcan be prevented from lowering.

FIG. 23 is a cross sectional view showing the essential section of the12th embodiment of the projection lens system of the present invention,and the same numeral is assigned to the part which is equivalent to apart shown in FIG. 21, and explanation is omitted.

Although the first communicating opening is installed in the outerbarrel 9 b of the lens barrel 9 in the aforementioned 11th embodiment,the 12th embodiment, as shown in FIG. 23, has a constitution thatjunction protrusions 26 are installed, for example, at three locationson one of the outer barrel 9 b and the bracket 11 or both of them, andthe outer barrel 9 b and the bracket 11 are joined at the junctionprotrusions 26, and a gap portion 27 a is provided in the portion otherthan the junction protrusions 26. Therefore, this gap portion 27 afunctions as the first communicating opening 27 connected from thespaces between the lens elements to the outside of the projection lenssystem.

FIG. 24 is a perspective view of the essential section showing theactual constitution of the first communicating opening 27 shown in FIG.23. In FIG. 24, the junction protrusions 26 are installed at threelocations on the end face of the bracket 11 and the gap portion 27 abetween the junction protrusions 26 is the first communicating opening27. The junction protrusions 26 may be installed on the flange surfaceat the end of the outer barrel 9 b instead of the end face of thebracket 11 or may be installed on both of them and put opposite to eachother free of substantial difference. In either case, the same effect asthat in the 11th embodiment can be obtained.

FIG. 25 is a cross sectional view showing the essential section of the13th embodiment of the projection lens system of the present invention,and the same numeral is assigned to the part which is equivalent to apart shown in FIGS. 21 and 23, and explanation is omitted.

A difference of the 13th embodiment from the 12th embodiment is a pointthat in the opening portions of the first communicating opening 27 andthe second communicating opening 28 toward the outside of the projectionlens system, a first flange 29 and a second flange 30 are arranged as adust-proof member respectively. In this case, assuming the communicatingopenings including portions along the dust-proof members 29 and 30 as acommunicating opening respectively, the shape of each communicatingopening itself can be regarded as a bent shape. In this embodiment, inaddition to the effects obtained in the 11th and 12th embodiments, sincethe system has a function for preventing a foreign material and lightfrom entering the projection lens system and light leakage from theprojection lens system, the contrast performance of the projection lenssystem itself will not be lowered and the image contrast of a rearprojection type image display apparatus using the projection lens systemwill neither be lowered. Even if a curved shape or twisted shape is usedas a shape of communicating opening in addition to the bent shape, thesame effect can be obtained.

FIG. 26 is a cross sectional view showing the essential section of the14th embodiment of the projection lens system of the present invention,and the same numeral is assigned to the part which is equivalent to apart shown in FIGS. 21, 23, and 25, and explanation is omitted.

A difference of the 14th embodiment from the 11th embodiment is a pointthat the lens barrel 9 is of an integrated type that it is not separatedinto an outer barrel and an inner barrel. In this embodiment, the secondcommunicating opening 28 is formed as a through hole inside the wallsurface of the lens barrel 9. Even if this constitution is used, thesame effect as that in the 11th and 12th embodiments can be obtained. Inthe same way as with the 13th embodiment, when a dust-proof member (notshown in the drawing) is installed in the opening portion of thecommunicating opening toward the outside of the projection lens system,the same effect as that in the 13th embodiment is obtained.

FIG. 27 is a cross sectional view showing the essential section of the15th embodiment of the projection lens system of the present invention,and the same numeral is assigned to the part which is equivalent to apart shown in FIGS. 21, 23, 25, and 26, and explanation is omitted. Adifference of the 15th embodiment from the 14th embodiment is a pointthat the second communicating opening 28 is formed as a through hole inthe neighborhood of the periphery of each lens element instead of athrough hole inside the wall surface of the lens barrel 9. Even if thisconstitution is used, the same effect as that in the 11th, 12th, and14th embodiments can be obtained. In the same way as with the 13thembodiment, when a dust-proof member (not shown in the drawing) isinstalled in the opening portion of the communicating opening toward theoutside of the projection lens system, the same effect as that in the13th embodiment is obtained.

Next, the constitution when the projection lens system as explained ineach aforementioned embodiment is used in a projection type imagedisplay apparatus will be explained.

FIG. 28 is a cross sectional view showing the essential section of thelongitudinal cross section of a rear projection type image displayapparatus using the projection lens system 17 of the present invention.Numeral 15 indicates a reflecting mirror, 16 a transmission type screen,21 a cabinet, and 22 a projection lens system holding member. The insideof the cabinet 21 is partitioned into an upper space 23 and a lowerspace 24 by the projection lens system holding member 22. The samenumeral is assigned to the part which is equivalent to a part shown ineach of FIGS. 21 to 27, and explanation is omitted.

In the rear projection type image display apparatus shown in FIG. 28,the aforementioned projection lens system 17 is held by the projectionlens system holding member 22 and the lens barrel 9, each lens elementtherein, and the bracket 11 are arranged in the upper space 23 in thecabinet. An original image displayed on the projection type cathode raytube 8 which is an image generating source is enlarged by the projectionlens system 17, and the optical path thereof is folded by the reflectingmirror 15, and the enlarged image is projected on the transmission typescreen 16.

When the projection lens system according to the lens data shown inTables 1 to 10 which is explained previously is used as a projectionlens system, a compact set can be realized as the rear projection typeimage display apparatus shown in FIG. 28.

FIG. 29 is a cross sectional view showing the longitudinal cross sectionof a rear projection type image display apparatus when the rearprojection type image display apparatus shown in FIG. 28 is structuredso as to stand on end as another embodiment of a rear projection typeimage display apparatus using the projection lens system 17 of thepresent invention. Numerals 23′ and 24′ indicate an upper space and alower space in the cabinet 21 respectively. The same numeral is assignedto the part which is equivalent to a part shown in FIG. 28.

FIG. 30 is a cross sectional view showing the projection lens system 17of the rear projection type image display apparatus shown in FIG. 28 indetail.

FIG. 31 is a cross sectional view showing the projection lens system 17of the rear projection type image display apparatus shown in FIG. 29 indetail.

The projection lens system 17 shown in FIGS. 30 and 31 has aconstitution equivalent to that of the 14th embodiment of theaforementioned projection lens system 17.

In the projection lens system 17 shown in FIG. 30, by the heat generatedby the projection type cathode ray tube 8 which is an image generatingsource, the lens element 20 a closest to the projection type cathode raytube 8 and the air in the space between the lens element 20 a and thelens element 20 b second closest to the projection type cathode ray tube8 are heated sequentially, and the heated air H at high temperatureflows out from the second communicating opening 28 formed in the lensbarrel 9 into the upper space 23, and on the other hand, low-temperatureair (open air) C flows in from the first communicating opening 27. Alsoin the projection lens system 17 shown in FIG. 31, by the heat generatedby the projection type cathode ray tube 8, the lens element 20 a closestto the projection type cathode ray tube 8 and the air in the spacebetween the lens element 20 a and the lens element 20 b second closestto the projection type cathode ray tube 8 are heated sequentially, andthe heated air H at high temperature flows out from the firstcommunicating opening 27 into the lower space 24′, and on the otherhand, low-temperature air (open air) C flows in from the secondcommunicating opening 28 formed in the lens barrel 9. By theseoperations, the efficiency of heat radiation from the lens elementsincreases, and the lens elements 20 a and 20 b are prevented from risingof temperature, and expansion and heat deformation are generated little,and the focus performance as a projection lens system is prevented fromchanging due to temperature.

The projection lens system 17 shown in FIGS. 30 and 31 may have theconstitution shown in another embodiment of the projection lens system17 and the same effect as that in the aforementioned case can beobtained. Furthermore, as shown in the 13th embodiment, when adust-proof member (not shown in the drawing) is installed in the openingportion of each communicating opening toward the outside of theprojection lens system, since the projection lens system 17 has afunction for preventing a foreign material and light from entering theprojection lens system and light leakage from the projection lenssystem, the image contrast of the rear projection type image displayapparatus will not be lowered.

In the above description, the constitution that each communicatingopening is arranged in the space between the lens element closest to theimage generating source and the lens element second closest to it ismainly explained. However, the location of each communication opening tobe arranged is not limited to it. Even if it is arranged in a spacebetween other lens elements, the same effect can be obtained though itis inferior slightly.

Only a case that the projection type cathode ray tube is used as animage generating source is explained. However, even if a constitutionthat a liquid crystal panel is combined with the light source is used,since the light source becomes a heat generating source, the same effectas the aforementioned can be obtained. Furthermore, as an example of theprojection type image display apparatus using the projection lens systemof the present invention, a rear projection type image display apparatusis explained. However, needless to say, even a case of a frontprojection type image display apparatus can obtain the same effect.

The present invention obtains many good results indicated below.

(1) Since a constitution that no concave lens is arranged on the screenside of the third lens having almost all the positive refractive powerof the overall projection lens system is used, even if the field angleis widened, distortion and astigmatism can be corrected and a high focusand a wide field angle are compatible with each other.

(2) Since a constitution that no concave lens is arranged between thethird lens having the positive refractive power and the first lensclosest to the screen side is used, the light focused in the marginalarea is not diverged between them. As a result, the height of light canbe lowered and a good marginal light amount ratio can be realized.

(3) Almost all the positive refractive power of the overall projectionlens system is shared by the third lens and by combination of localaspherical surface profiles of the first and second lenses, the loweringof the focus performance due to changes in temperature and absorption ofmoisture can be reduced.

(4) When a lens having negative refractive power with the concavesurface facing the screen side is installed in the location closest tothe projection tube which is an image light source as a sixth lens andthe lens surface of the lens on the screen side is formed as a profilethat the lens refractive power in the area through which the light fluxfrom an object in the marginal area on the fluorescent face passes isweaker than that in the neighborhood of the optical axis of the lens,the difference in length of optical path between the saggital plane andthe meridional plane is made smaller. Furthermore, in a lens arrangednext on the screen side to the above-mentioned lens having negativerefractive power, when the profile of the lens surface on the projectiontube side is convex on the projection tube side in the neighborhood ofthe optical axis and concave on the projection tube side in the marginalarea, the above difference in length of optical path can be made moresmaller and the astigmatism in the marginal area can be corrected withhigher precision.

(5) The third lens is an inexpensive low dispersion glass convex lensand the cost of the overall projection lens system is reduced. Tocorrect chromatic aberration, the fourth lens is a high dispersionplastic concave lens and used in combination with the third lens.Furthermore, a filter for cutting the spurious component other than thedominant wavelength component of the light emission spectrum of aphosphorescent substance is installed in at least one lens of the lensesconstituting the projection lens system and the generated chromaticaberration itself is reduced.

(6) Furthermore, to realize a large aperture, the aforementioned fourthlens is a large dispersion plastic concave lens, and the profile thereofis formed in a protile of strong aspherical surface, and the aberrationcan be corrected with high precision.

The entry height of the upper ray into the third lens (glass lens) canbe lowered by the aspherical surface profile of the fourth lens, so thatthe diameter of the third lens (glass lens) can be decreased for thesame F-number and the cost can be reduced.

Furthermore, the incident angle of the upper ray into the third lens(glass lens) can be increased, so that the refractive power of the thirdlens 3 can be made smaller. As a result, an inexpensive glass materialwith a refractive index nd of 1.6 or less can be used and the cost canbe reduced.

When the aforementioned projection lens system is used, a bright andhigh focus image can be obtained in the overall area of the screen and acompact projection type display apparatus can be realized. When theprojection lens system of the present invention is applied, between thedistance (projection distance) L (mm) from the top of the lens surfaceof the lens closest to the screen in the first lens on the screen sideto the transmission type screen and the diagonal effective size M (inch)of the transmission type screen, the following relation is held:

17.3<(L/M)<17.6

and a compact set can be realized.

On the other hand, according to the present invention, when thecommunicating opening or communicating window explained in eachaforementioned embodiment is arranged in the lens barrel of theprojection lens system or others, the efficiency of heat radiation fromthe lens elements is increased by the convection action of air, and thelens elements are suppressed in rising of temperature, and the expansionand deformation due to rising of temperature are suppressed, and as aresult, the lens performance, particularly the focus performance areprevented from lowering.

Furthermore, when a dust-proof member in a shape such as a flange isarranged in a suitable location of the opening portion of theaforementioned communicating opening or communicating window toward theoutside of the projection lens system or when the communicating openingor communicating window itself is formed in a bent, or curved, ortwisted shape, entry of a foreign material or light into the projectionlens system and light leakage from the inside of the projection lenssystem are prevented, and the contrast performance of the projectionlens system itself will not be lowered, and the image contrast of aprojection type image display apparatus using the projection lens systemwill be neither reduced.

What is claimed is:
 1. A projection lens system for enlarging anddisplaying on a screen an original image displayed on a fluorescent faceof a projection tube, said lens system comprising a plurality of lenselements, among which a lens element disposed nearest said projectiontube is a concave meniscus lens having a concave lens surface facingsaid screen, wherein: said concave meniscus lens is connected to saidprojection tube by a liquid coolant for cooling said projection tube;and said concave meniscus lens has profile such that refractive power ata marginal area adjacent a periphery of said concave meniscus lens isless than the refractive power at an area adjacent optical axis of saidprojection lens system.
 2. A projection lens system according to claim1, wherein said plurality of lens elements includes at least a firstaberration correction lens disposed closest to said screen and a convexlens having a strongest refractive power among said lenses other thansaid concave meniscus lens, being disposed between said first aberrationcorrection lens and said concave meniscus lens.
 3. A projection lenssystem according to claim 2, further comprising a second aberrationcorrection lens disposed between said convex lens and said concavemeniscus lens.
 4. A projection lens system according to claim 3, whereinsaid second aberration correction lens has a lens surface on a sidefacing said projection tube, which is in said area adjacent said opticalaxis, and is concave in said marginal area.
 5. A projection lens systemaccording to claim 4, wherein said second aberration correction lens isdisposed prior to and adjacent said concave meniscus lens.
 6. Aprojection lens system for enlarging and displaying on a screen anoriginal image displayed on a fluorescent face of a projection tube,said lens system comprising a plurality of lens elements, among which alens element disposed nearest said projection tube is a concave meniscuslens whose concave surface faces said screen, wherein: said concavemeniscus lens is connected to said projection tube by a liquid coolantfor cooling said projection tube; refractive power of said concavemeniscus lens increases along a radially outward direction from anoptical axis of said projection lens system to a point between saidoptical axis and a marginal area adjacent a periphery of said concavemeniscus lens, and decreases outwardly from said point to said marginalarea; and refractive power in said marginal area of said concavemeniscus lens is less than refractive power adjacent said optical axis.7. A projection image display apparatus having a screen, a projectiontube and a projection lens system for enlarging and displaying on thescreen an original image displayed on a fluorescent face of theprojection tube, wherein: said projection lens system comprises aplurality of lens elements, among which a lens element disposed nearestsaid projection tube is a concave meniscus lens having a concave lenssurface facing the screen: said concave meniscus lens has a profile suchthat refractive power at a neighborhood of a marginal area adjacent aperiphery of said concave meniscus lens is less than refractive poweradjacent an optical axis of said projection lens system; and a liquidcoolant for cooling said projection tube is filled between said concavemeniscus lens and the fluorescent face of said projection tube; wherebya negative lens is formed by said concave meniscus lens, saidfluorescent face of said projection tube and said liquid coolant.